Sorry I was trying to point you toward the 223. So many people try to load a round to the max, and it would be better to just buy the next size up. The k Hornet just does not gain enough to make it worth the work for me. A 218 bee is my next chioce after the Hornet, but the Hornet is usually what I pick up to shoot. I love handguns, and the Hornet. It is easy to load for. and the 10" barrel is easy to carry and shoot. The noise is not as bad as the 223, and my old gun groups as well as most rifles.
To rechamber a Contender barrel I remove the dove tail forend screw holders. Tape the extractor down to keep the extractor groove solid. Chuck it in a lathe, use a good cutting oil, and run the reamer in a little at a time. Removing it to flush the metal from it and the barrel every 1/4 " or so. A good sharp reamer cuts clean and quick, don't let it load up with metal. Your cutting a chamber for a barrel that you will use for years, why be in a hurry. As the saying goes "IF you don't have time to do it right you don't have time to do it". It is possibly to cut one by hand. Reamers like Dave Kiff , at Pacific tool and gauge, and others make have a square shank that you can turn by hand. The chamber is usually smoother with a lathe set up, but I have cut small case chambers by hand with good results. I buy the reamers I use, and have them cut to the specs. I want. You can rent reamers in standard and a lot of wildcat chamberings for a few dollars a day. Good luck, hope this helps answer some of your questions.